RF Power Density vs Distance

The RF power density at any distance from a transmitter that is radiating RF power will depend upon the antenna gain, power into the antenna, and the distance from the antenna. The table below illustrates haw fast the RF power power density drops off given certain distances from the radiating antenna and the power into the antenna.

11 meters from a 125 watt transmitter is about the same RF power density as 1 meter from a 2 watt transmitter.

Power (dBm)

Power (Watts)

Antenna Gain (dBi)

Antenna Gain Factor

Distance (meters)

PSD(W/m2)

20

0.10

0

1

0.1

0.796

20

0.10

0

1

0.5

0.032

20

0.10

0

1

1

0.008

20

0.10

0

1

3

0.001

20

0.10

0

1

10

0.000

30

1.00

0

1

0.1

7.962

30

1.00

0

1

0.5

0.318

30

1.00

0

1

1

0.080

30

1.00

0

1

3

0.009

30

1.00

0

1

10

0.001

33

2.00

0

1

0.1

15.886

33

2.00

0

1

0.5

0.635

33

2.00

0

1

1

0.159

33

2.00

0

1

3

0.018

33

2.00

0

1

10

0.002

36

3.98

0

1

0.1

31.696

36

3.98

0

1

0.5

1.268

36

3.98

0

1

1

0.317

36

3.98

0

1

3

0.035

36

3.98

0

1

10

0.003

42

15.85

0

1

0.1

126.186

42

15.85

0

1

0.5

5.047

42

15.85

0

1

1

1.262

42

15.85

0

1

3

0.140

42

15.85

0

1

10

0.013

51

125.89

0

1

0.1

1002.329

51

125.89

0

1

0.5

40.093

51

125.89

0

1

1

10.023

51

125.89

0

1

3

1.114

51

125.89

0

1

10

0.100

54

251.19

0

1

0.1

1999.910

54

251.19

0

1

0.5

79.996

54

251.19

0

1

1

19.999

54

251.19

0

1

3

2.222

54

251.19

0

1

11

0.165

Filed under: Engineering | Posted on December 26th, 2012 by John Sonnenberg